1. Field of the Invention
The present invention relates to a recliner adjuster attached to, for example, an automobile seat for appropriately adjusting inclination of a seat back with respect to a seat cushion.
2. Description of the Related Art
Conventional reclining seats are provided with a recliner adjuster interposed between a seat cushion and a seat back hingedly connected to the seat cushion. The recliner adjuster includes a first bracket fixed to one of the seat cushion and the seat back, and a second bracket fixed to the other of the seat cushion and the seat back and mounted on the first bracket so that one of the first and second brackets can rotate relative to the other.
The recliner adjuster also includes a cam interposed between the first and second brackets and fixed to a support shaft that is concentrically aligned with a center of rotation of the one of the first and second brackets relative to the other. Rotation of the support shaft rotates the cam, which in turn causes a lock plate to slide radially outwardly or inwardly between the first and second brackets. The first bracket has a radially extending guide groove having opposite parallel side walls. The lock plate has teeth formed on an outer periphery thereof and is slidably disposed within the guide groove.
On the other hand, the second bracket has internal teeth concentrically formed around the center of rotation referred to above. When the lock plate slides radially outwardly along the guide groove upon rotation of the cam together with the support shaft, the teeth of the lock plate are brought into engagement with the internal teeth of the second bracket, resulting in locking of the first and second brackets. Reverse rotation of the cam releases the engagement of the teeth of the lock plate with the internal teeth of the second bracket, thus allowing the one of the first and second brackets to rotate relative to the other.
Accordingly, when an operating rod connected to the support shaft is operated, the teeth of the lock plate engage with the internal teeth of the second bracket to retain inclination of the seat back, or the teeth of the lock plate disengage from the internal teeth of the second bracket so that inclination of the seat back can be changed as desired.
In the above-described conventional recliner adjuster, there exist several sliding portions between the lock plate and the opposite side walls of the guide groove, or between the cam and the lock plate, and such sliding portions have respective clearances, though they are slight. Accordingly, when a load is applied to the seat back, the lock plate inclines in a direction of the load, and a strength of engagement of the teeth of the lock plate with the internal teeth of the second bracket becomes weak, thereby making it impossible to obtain a positive locking condition.
To solve this problem, it is conceivable that accuracy in size of the guide groove and the lock plate be enhanced to reduce clearance between the lock plate and the opposite side walls of the guide groove as much as possible. However, this requires considerably accurate metal working with respect to the lock plate and the like, thereby giving rise to another problem of costs increasing.
In view of the above, the applicants of the present invention have hitherto proposed an improved recliner adjuster wherein the lock plate has a projection integrally formed therewith that is, when a load is applied to the seat back under a condition in which teeth of the lock plate are held in engagement with internal teeth of a second bracket, brought into contact with an inner edge of a guide groove to prevent the lock plate within the guide groove from inclining in the direction of the load (see Japanese Laid-Open Patent Publication No. 2000-342370).
According to this recliner adjuster, the load applied to the seat back is transmitted to the teeth of the lock plate via the internal teeth of the second bracket to incline the lock plate within the guide groove, but a force that acts to incline the lock plate is cancelled by contact of the projection with the inner edge of the guide groove, thereby preventing the lock plate from inclining. Accordingly, deterioration in engagement between the teeth of the lock plate and the internal teeth of the second bracket, which may be caused by inclination of the lock plate, is avoided, thereby making it possible to retain the seat back in position.
In the recliner adjuster as disclosed in Japanese Laid-Open Patent Publication No. 2000-342370, however, if a large load that exceeds an allowable load is applied to the seat back, and the lock plate pushes excessively one of the side walls of the guide groove to increase a surface pressure thereof, there is a possibility of the lock plate inclining largely due to deformation of such side wall of the guide groove. Inclination of the lock plate makes engagement between the teeth of the lock plate and the internal teeth of the second bracket weak, thus lowering locking strength.